The CData Cmdlets PowerShell Module for Microsoft SharePoint supports standard SQL joins like the following examples.

Inner Join

An inner join selects only rows from both tables that match the join condition:

SELECT d.LinkFileName, u.Name FROM Documents d, Users u WHERE d.CheckOutUser = u.Name

Left Join

A left join selects all rows in the FROM table and only matching rows in the JOIN table:

SELECT d.LinkFileName, u.Name FROM Users u LEFT JOIN Documents d ON d.CheckOutUser = u.Name